Paint spray gun nozzle heads of the type closed by a needle valve are used with high-pressure guns which are operated with compressed air pressure of about 4 bar. This results in very fine spraying of the paint. However a paint mist forms which is harmful to the gun user. The user of these nozzle heads works with high air pressure and a relatively small quantity of air.
In a spray gun known by the name "SATAjet", the circular jet air nozzle of its nozzle head has an outlet area of 2 to 3 mm.sup.2 from which the air issues at a high speed, and flows past a small spigot projecting about 0.1 mm beyond the outlet area. Paint from the paint nozzle is thereby drawn and atomized. The finer the spray, the stronger is the mist formation, i.e. the portion of atomized paint which issues from the actual paint jet. The air issuing from the circular jet air nozzle forms a sharply defined circular jet which fans out over a distance from the nozzle head. In the region of the nozzle head, the outside of the circular air jet has a very high speed relative to the ambient air. The paint is accelerated to relatively high speed while being sprayed.
In order to reduce the mist formation, low-pressure guns are used which are operated at an air pressure of 0.7 bar maximum and using a large quantity of air. Low-pressure guns of this type are, for example, the subject of German patent documents DE-A 28 22 650 and DE-A 33 18 204. A common feature of these guns is that the compressed air issuing from the circular jet air nozzle issues at a low pressure and large volume. For this reason, the outlet area of the circular jet air nozzle has an area of about 15 mm.sup.2. The paint jet is thereby surrounded by an air cone which, to a great extent, prevents paint mist from being issued. In this case, however, one must put up with only inadequately sprayed paint which reaches the surface to be coated in the form of relatively large drops. Some of these drops leave the spray jet and fall down, which can be clearly seen on paper placed on the floor below the jet.